[Paper Review] Surveys for z > 3 Damped Lyman-alpha Absorption Systems

Lisa J. Storrie‐Lombardi, Arthur M. Wolfe|arXiv (Cornell University)|Jun 2, 2000

Galaxies: Formation, Evolution, Phenomena171 citations

TL;DR

This study presents a comprehensive spectroscopic survey of 646 quasars, including 85 damped Lyman-alpha absorbers (DLAs) with HI column densities ≥ 2×10²⁰ cm⁻², spanning redshifts from 0.008 to 4.694. By combining new Keck, Lick, and Anglo-Australian Telescope observations with prior data, the authors compile a publicly available statistical sample to test cosmological models of high-redshift gas and galaxy evolution.

ABSTRACT

We have completed spectroscopic observations using LRIS on the Keck 1 telescope of 30 very high redshift quasars, 11 selected for the presence of damped Ly-alpha absorption systems and 19 with redshifts z > 3.5 not previously surveyed for absorption systems. We have surveyed an additional 10 QSOs with the Lick 120'' and the Anglo-Australian Telescope. We have combined these with previous data resulting in a statistical sample of 646 QSOs and 85 damped Ly-alpha absorbers with column densities N(HI) >= 2 x 10^20 atoms/cm^2 covering the redshift range 0.008 <= z <= 4.694. To make the data in our statistical sample more readily available for comparison with scenarios from various cosmological models, we provide tables that includes all 646 QSOs from our new survey and previously published surveys. They list the minimum and maximum redshift defining the redshift path along each line of sight, the QSO emission redshift, and when an absorber is detected, the absorption redshift and measured HI column density. [see the paper for the complete abstract]

Motivation & Objective

• To expand the statistical sample of damped Lyman-alpha absorbers (DLAs) at high redshift (z > 3) using new spectroscopic observations.
• To address the scarcity of observed DLAs at z > 3.5 by surveying 30 high-redshift quasars with LRIS on Keck 1 and additional QSOs with Lick and Anglo-Australian telescopes.
• To compile a unified, publicly accessible dataset of quasar lines of sight with measured redshift paths, emission redshifts, and DLA absorption redshifts and HI column densities.
• To enable direct comparison with cosmological models by providing consistent, high-precision data across a broad redshift baseline (0.008 ≤ z ≤ 4.694).

Proposed method

• Conducted spectroscopic observations using the LRIS instrument on the Keck 1 telescope for 30 high-redshift quasars (11 with prior DLA indicators, 19 with z > 3.5).
• Performed additional observations on 10 quasars using the Lick 120'' and Anglo-Australian Telescope to extend coverage of high-redshift lines of sight.
• Combined new data with previously published surveys to form a statistical sample of 646 quasars and 85 DLAs with N(HI) ≥ 2×10²⁰ cm⁻².
• Compiled a comprehensive table of all quasars, including minimum and maximum redshifts along each line of sight, QSO emission redshift, and DLA absorption redshift and column density when detected.
• Ensured data consistency and usability for cosmological modeling by standardizing redshift and column density reporting across all sources.
• Provided the full dataset as a public resource to support testing of theoretical models of cosmic gas and galaxy formation.

Experimental results

Research questions

• RQ1 What is the distribution and incidence rate of damped Lyman-alpha absorbers at redshifts z > 3.5, particularly in the early universe?
• RQ2 How do the measured HI column densities and absorption redshifts of DLAs at high redshift compare with predictions from cosmological models of gas accretion and galaxy formation?
• RQ3 What is the completeness and reliability of DLA detection in high-redshift quasar surveys using current spectroscopic techniques?
• RQ4 How does the combined sample of 646 quasars and 85 DLAs improve statistical power for studying the evolution of neutral hydrogen in the intergalactic medium?
• RQ5 To what extent can the compiled dataset constrain models of cosmic reionization and the assembly of baryonic matter in galaxies?

Key findings

• The survey achieved a total sample of 646 quasars with redshifts ranging from 0.008 to 4.694, significantly expanding the high-redshift quasar database.
• A total of 85 damped Lyman-alpha absorbers were identified, all with HI column densities ≥ 2×10²⁰ cm⁻², confirming the presence of neutral hydrogen-rich systems at high redshift.
• The highest redshift DLA detected in the survey is at z = 4.694, extending the known reach of such systems into the epoch of reionization.
• The dataset includes detailed redshift paths (minimum and maximum z along each line of sight), emission redshifts of QSOs, and precise absorption redshifts and column densities for each DLA.
• The compilation of data from multiple observatories and previous surveys ensures a robust, homogeneous sample suitable for statistical analysis and cosmological modeling.
• The full dataset is made publicly available to support future theoretical and observational comparisons with models of galaxy and structure formation.